#include<stdio.h>

int fac(int x)
{
	int sign,pro=1;
	for(sign=2;sign<=x;sign++)
	{
		pro*=sign;
	}
	return pro;
}
int main()
{
	int m,n;
	scanf("%d %d",&m,&n);
	float p=1.0*fac(m)/fac(n)/fac(m-n);
	printf("%.2f",p);
	return 0;
}
